The invention relates to vapor generator wall-supported gas plenums and more particularly to an arrangement for protecting the wall from stresses resulting from thermal expansion of the plenum and duct sections associated therewith.
The modern central station vapor generator includes a furnace or combustion chamber defined by upright walls commonly known as membrane walls and formed of upwardly extending laterally spaced fluid conducting tubes rigidly united by metallic webs throughout substantially all of their length. The burners and windboxes or air plenums are located along the lower portion of the furnace to deliver the fuel and air required to generate the combustion gases which heat the fluid being conducted through the wall tubes. A regulated quantity of combustion gases is recirculated to the furnace via gas tempering and/or recirculating plenums to minimize slag deposition and control vapor temperature.
The plenums are box-like enclosures and are outwardly mounted on the furnace wall. A duct is connected to opposite ends of each plenum to supply combustion air or recirculated gases therethrough to the furnace. The discharge portions of the ducts are connected to fixed supports and include end sections extending from the support to the plenum connections. Each of the end sections is normally provided with a pair of spaced and outwardly corrugated expansion joints which are intended to accommodate the movement due to thermal expansion of the plenum and duct end sections.
A problem has arisen with the prior art construction when applied to membrane walls, these have been known to buckle and tear as a result of stresses generated by the expansion movement of the ducts and plenum while overcoming the initial resistance of the corrugated joints. A further problem has been encountered as a result of stress buildup due to the eventual malfunction of duct floor related expansion joints caused by deposition of particulates in the corrugation groove